Smita Chaubey

Turnaround-Point Long-Period Fiber Gratings (TAP-LPGs) as High-Radiation-Dose Sensors

This letter reports the application of turnaround-point (TAP) long-period gratings (LPGs) for radiation dosimetry. The LPGs were realized using the laser-writing technique. After a gamma dose of 6 kGy, the TAP-LPGs show a radiation-induced shift of more than 35 nm for each of the dual resonance dips, which is the highest shift reported to date for any type of fiber gratings. These LPGs can therefore be used as radiation sensors down to doses of a few Gy with modest wavelength-resolving instrumentation. The LPGs show significant sensitivity of wavelength shifts up to 80 nm for a dose of 65 kGy. We attribute the very high radiation sensitivity to near-TAP operation and doping of Boron in the fiber. This should open up applications of LPGs to radiation dosimetry.

Detection of Fuel Adulteration With High Sensitivity Using Turnaround Point Long Period Fiber Gratings in B/Ge Doped Fibers

We report for the first time the application of turnaround-point long period fiber gratings for wavelength encoded detection of automobile fuel adulteration. The demonstrated high sensitivity of 0.96 nm/% change of kerosene in petrol up to 10% adulteration is significantly high compared with previously published values. These specialty gratings can easily detect the presence of 1% contamination of kerosene in petrol and thus provide opportunities for development of portable fuel adulteration sensors.

Measurement of

We propose a novel approach to measure in-situ refractive index changes induced by gamma radiation in single mode fibers. The changes are derived from wavelength shifts of resonances of a CO2 laser written long period fiber grating. Using this approach, we estimate the radiation induced refractive index increase in the core of B/Ge co-doped fiber as 2.1×10-5 at 10 kGy and 1.85×10-4 at 1.54 MGy. At doses , the index changes are considered to be governed by glass polarizability changes. Numerical simulations show that saturation of the index change can be observed at doses . Irradiation has a negligible effect on the resonance dip strengths and bandwidths, with the exception of the turnaround point mode.

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Turn around point (TAP) in long period fiber grating (LPG) provides extremely high sensitivity to external environmental parameters like temperature, strain and refractive index. It also opens up new dimensions for development of photonic devices. Higher order cladding mode coupling in a LPG requires relatively lower grating period (< 300 µm), which can be achieved by improving the spot size in CO2 laser based grating inscription methods. But the inscription of LPG with resonance exactly at TAP within 950–1700 nm wavelength band requires a period precision better than 0.5 µm. Since, our fabrication system based on automated CO2 laser has limited translational resolution, we have used exposure to gamma radiation and tapering of fiber as tools to tailor the spectral characteristics of our gratings. Total Gamma radiation exposure of about 6 kGy resulted in ± 35nm wavelength shift of dual resonant loss peaks in a 206 µm period near TAP-LPG, almost merging the two peaks. This exposed LPG was then tapered using CO2 laser for exact TAP operation. Amplitude based strain sensitivity of 1.13dB/me was obtained with tuned TAP LPG.

-Radiation Induced Refractive Index Changes in B/Ge Doped Fiber Using LPGs

This article discusses a digital filtering technique to improve the temperature resolution of a Raman fiber optic distributed temperature sensor. A frequency-domain digital filtering algorithm has been used for this typically time-domain task to show that by reducing the effect of noise introduced by analog electronics and the quantization noise of the analog-to-digital converter in the detection and data acquisition stages, superior temperature resolution is achievable. An important feature of the filtering scheme used is that no spatial inaccuracy is introduced into the ranging of hot zones, despite the highly nonlinear phase response of the filter. Digital filtering used for postprocessing of data shows clearly and unambiguously a temperature resolution of 5 K in the present setting of our experiment, with the possibility of much greater improvement. Merely using analog signal conditioning does not provide the same clarity and uniqueness in temperature resolution and spatial location that digital filtering offers. This digital filtering scheme offers greater flexibility and versatility than mere signal-averaging approaches to improve the SNR of such systems. The filters ability to reject deterministic interfering frequencies of appreciable energy content is also demonstrated by simulating such frequencies of much greater energy than the actual signal.

Radiation and taper tuning of Long Period Grating for high sensitivity strain measurement

This is the first report, to the best of our knowledge, of synchrotron X-ray beam induced writing of long-period fiber gratings in photosensitive silica optical fibers. We demonstrate efficient writing and significant index changes in optical fiber. These gratings were found to be highly resistant to gamma radiation and can be used for temperature sensing applications in high dose nuclear radiation environment.

Bidirectional frequency-domain digital filtering to simultaneously improve temperature resolution and eliminate spatial inaccuracy of a distributed temperature sensor

We have experimentally studied in real time the effect of gamma radiation on the characteristics of long period fibre gratings written in different types of fibres. The grating parameters and fibre composition have been optimized. Prototype packaged sensors have been developed for field application.

Long Period Fiber Grating Written by Synchrotron X-Ray Radiation

We present for first time the detailed investigation on the effect of MGy (106 Gy) dose level of gamma radiation on the parameters of CO2 laser-written long-period fiber gratings (LPFGs) in B/Ge-doped single-mode fibers with particular attention to lower-order modes and higher order nonturnaround point (non-TAP) modes. Wavelength shifts up to 11 nm for 100 kGy dose and a further shift of 20 nm (1.5 nm/100 kGy) for dose of 900 kGy (total 1 MGy) were observed. Further, the radiation-induced shifts of resonant modes did not saturate up to a 1 MGy dose. No remarkable changes were observed in width and amplitude of the resonant dips during in-situ measurements up to the full dose irradiation. The radiation sensitivity up to 100 kGy was found to be independent of the grating period. This study shows that LPFGs in boron-doped fibers are strong candidates for very high-dose sensing applications such as in super Large Hadron Collider (LHC) and International Thermonuclear Experimental Reactor (ITER).

Investigation of nuclear radiation sensing potential of fibre gratings with special reference to nuclear reactors and accelerators

Multi-parameter sensing specialty fiber gratings are of crucial importance for nuclear industry due to their unique properties such as high radiation dose sensitivity, viability of operation up-to 1 MGy dose. We report on our unique in-situ dose measurements of Turnaround-point LPGs and their applications for strain and temperature measurements.